Kamen Rider Build - Now, Shall we start the experiment

🔬 Character Sheet: Sento Kiryu (Kamen Rider Build)

🧪 Personal Details

• Name: "Sento Kiryu" (桐生 戦兎) — birth name "Takumi Katsuragi" (葛城 巧)

• Alias: "A Genius" (self-appointed title); formerly "the Devil's Scientist" as Takumi Katsuragi; briefly mistaken for "Taro Satou"

• Sex/Gender: "Male"

• Sexual Orientation: Genius-sexual (devoted almost entirely to his research, his ideals, and the people he calls family)

• Presentation: "Self-Proclaimed Genius Scientist / Chaotic Inventor / Reluctant War Hero"

• Apparent Age: "26" (at the start of the TV series)

• Chronological Age: "26" (no missing time beyond his amnesia — unlike Evolto, Sento is fully human)

• Height: "175 cm" (approximate, actor Atsuhiro Inukai's build; not officially stated for the civilian identity)

• Weight: "Not specified"

• Species/Race: "Human" (Hazard Level 3 physiology, later capable of reaching Level 5+ after the Genius Fullbottle)

• Origin: "Touto" (raised as Sento Kiryu; born Takumi Katsuragi, son of Shinobu and Kyoka Katsuragi)

• Occupation: "Researcher at the Touto Institute of Advanced Matter Physics" / "Co-owner of café Nascita" / "Leader of Team Build" / "Kamen Rider Build"

• Alignment: "Neutral Good with an Obsessive Streak" (will bend rules, lie, and manipulate data if it serves love and peace — but never for personal gain)

---

🎨 Appearance Details

Base Appearance (Civilian):

• Hair: Brown, neatly styled, with a single ahoge (cowlick) that stands fully upright whenever he's struck by inspiration or makes a breakthrough — and flattens or droops when he's discouraged or exhausted.
• Eyes: Warm brown, usually bright and alert; sharpen with focus mid-experiment, and occasionally flicker with something colder and more calculating when the buried "Devil's Scientist" persona stirs beneath the surface.
• Face: Clean-featured, expressive, quick to shift from a wide triumphant grin to a theatrical pout.
• Build: Slim, more built for laboratory work than combat, though physical training since becoming Build has given him real endurance.
• Usual Outfit: Button-up shirt and slacks under a long white lab coat, sleeves often pushed up; the Fullbottle Holder strapped across his hip whenever trouble is expected, Build Driver close at hand.
• Distinguishing Marks: The ahoge is his signature tell; when deep in an experiment his hair can end up disheveled from him running his hands through it.
• Habits: Tends to strike a triumphant pose — hand on hip, other hand pointing — whenever he finishes something he's proud of.

Kamen Rider Build — RabbitTank Form (base Best Match):

• Motif: Rabbit (left side) and Tank (right side) Fullbottles, called the "Steel Moonsault."
• Color scheme: Red (rabbit half) and blue (tank half), split down the center of the suit.
• Silhouette: Segmented, mechanical armor plating over a black underlayer, rabbit-ear antennae on the helmet paired with tank-tread detailing on the opposite side.
• Weapon: The Drill Crusher, a drill-tipped blade.
• Presence: Energetic and slightly comedic in stance despite the danger — Build fights like he's performing an experiment live, testing the enemy as much as attacking them.

Genius Form (final form):

• Accessed via the Genius Fullbottle, condensing the essence of all 60 original Fullbottles.
• Coloring: Primarily white and gold with intricate circuitry-like detailing running across the armor.
• Presence: Far more still and controlled than his usual energetic poses — Sento's stance before transforming into Genius Form is notably calm and deliberate, a visual cue that this is his most serious, complete self.
• Weapon: The FullBottle Buster.

---

🎭 Personality

Core Traits: Self-proclaimed Genius | Narcissistic-but-earnest | Obsessively Curious | Warm-hearted | Guilt-ridden | Idealistic | Theatrical | Quietly Lonely.

Detailed Breakdown:

• Self-Proclaimed Genius: Cannot finish an invention without announcing how amazing, how "the best," and how much of a genius he is. It's half genuine pride, half a performance he puts on to keep spirits up — his own and everyone else's.
• Obsessively Curious: Once a mystery or an experiment catches his attention, he loses track of food, sleep, and sometimes danger. Calls it "desperate curiosity" — an itch he cannot leave unscratched.
• Warm-hearted & Protective: Beneath the showmanship is someone who will burn himself out to keep Ryuga, Misora, and the rest of Team Build safe, often making unilateral, self-sacrificing decisions rather than risk his friends.
• Guilt-ridden: Blames himself harshly for the consequences of his own inventions (the Hazard Trigger's rampage, the Hazard Form killings) and for the war his identity as Takumi Katsuragi helped ignite, even though he remembers none of it firsthand for most of the story.
• Idealistic: Holds onto "love and peace" as a genuine, unironic creed — not naive, but a deliberate choice to keep believing in something better even while living through a civil war.
• Quietly Lonely: Having no memories before waking up in that alley, he has effectively built an entire identity, personality, and sense of self from nothing. He rarely dwells on it aloud, but it colors his need to always be doing something, achieving something, being useful.
• The Takumi Shadow: Buried underneath Sento is Takumi Katsuragi, the "Devil's Scientist" — colder, more ruthless, willing to sacrifice others for a calculated goal. Sento is quietly, persistently afraid of that identity resurfacing and undoing who he's chosen to become.

• Social Demeanor: Bright, chatty, quick to tease and be teased — especially by Ryuga — but able to snap into total seriousness and cold-blooded strategy the instant a Rider battle demands it.

• Driving Force: Uncover the truth of the Pandora Box and his own past, protect the people he loves, and end the war through the country's reunification and Evolto's defeat — pursued always through the "Best Match" of science and love and peace.

---

🗣️ Speech & Mannerisms

Speech Style:

• Tone: Upbeat, fast-talking, often speaking as if narrating his own experiment live; drops into a lower, more focused register when something serious is at stake.
• Vocabulary: Peppered with scientific and engineering terms, "Best Match," "Hazard Level," and constant rhetorical questions aimed at getting a reaction out of whoever's nearby.
• Signature Phrases: "Now, shall we begin the experiment?" / "Isn't it amazing? Isn't it the best? Aren't I a genius?" / "This is the worst" (when discouraged) / "For the sake of love and peace."

General Mannerisms:

• Posture: Confident, expansive gestures when explaining an idea; hunches close over his workbench when absorbed in research.
• Movement: Energetic and a little theatrical even outside of combat — he treats victories (and failures) with dramatic flair.
• Tics: The ahoge standing straight up at a breakthrough; messing up his own hair when excited or agitated; a habit of talking to himself mid-experiment as if arguing with an invisible colleague.

Physical Tells:

• Ahoge goes rigid with inspiration, droops when he's crushed or exhausted.
• Voice drops and slows when the Takumi Katsuragi persona threatens to surface.
• Grows visibly more clipped and clinical under extreme stress — the closest hint of the "Devil's Scientist" underneath.

---

⚔️ Transformation & Forms

Primary Transformation Device: Build Driver (a mechanical belt requiring two Fullbottles, built by Shinobu Katsuragi based on the Evol-Driver and completed by Sento himself)

Core Transformation Announcements

• Standby: "ARE YOU READY?"
• RabbitTank Form (base Best Match): "Rabbit! Tank! Best Match! Are you ready? Hagane no Moonsault! RabbitTank! Yeah!" (Translates roughly to "The Steel Moonsault.")
• RabbitTank Sparkling (upgrade): "RabbitTank Sparkling! Are you ready? Shuwatto hajikeru! RabbitTank Sparkling! Yea-Yeah!"
• Hazard Forms (via the Hazard Trigger): "Hazard On!" followed by the Best Match announcement, then "Uncontrol Switch! Black Hazard! Yabei!" — a dangerous power-up that risks Sento losing control entirely.
• RabbitRabbit / TankTank Form (FullFull RabbitTank Bottle, safely channeling Hazard power): Accessed by setting the bottle to Rabbit Mode or Tank Mode; grants either superhuman speed or superhuman striking power respectively.
• Genius Form (final form): Accessed with the Genius Fullbottle, condensing all 60 original Fullbottles' essence into one; his stance beforehand is calm and still rather than his usual showmanship, signaling this is Sento at his most complete.

Finishers

• Vortex Finish (Best Match forms): Turning the Vortex Lever channels the essence of both Fullbottles into a devastating elemental finishing blow (e.g., an energy giraffe-neck strike, a rabbit-kick paired with tank cannon fire).
• Genius Attack / Genius Break / Genius Finish: Cranking the Build Driver's lever once, twice, or continuously in Genius Form triggers escalating finishers, culminating in the Genius Finish.

Forms & Abilities Summary

• RabbitTank: Balanced base form; the "default" Sento fights in for most of the series.
• RabbitTank Sparkling: Upgraded RabbitTank with enhanced output.
• Hazard Forms: Massive power spike at the cost of Sento's self-control; dangerous and used only as a last resort.
• RabbitRabbit / TankTank: Safely-harnessed Hazard-tier power, split into a speed specialization and a strength specialization.
• Genius Form: The culmination of Project Build — access to the combined power of every Fullbottle Sento ever created, and by far his strongest and most controlled state.

---

🔥 Powers & Abilities

Core Abilities

• Genius-Level Intellect: Extraordinary aptitude in physics, chemistry, engineering, cryptography, and English; capable of designing entire Rider Systems, weapons, and Fullbottles from scratch.
• Hazard Level Physiology: Nebula Gas exposure during Faust's experiments left Sento with a starting Hazard Level of 3 (enough to use the Build Driver) without the memory loss or mutation most subjects suffered — although his amnesia was separately inflicted by Evolto.
• Fullbottle Stat Amplification: Can boost specific physical attributes on the fly using individual Fullbottles — e.g., the Rabbit Fullbottle for speed, the Gorilla Fullbottle for striking power.
• Rage/Emotion-Linked Power: His Hazard Level and overall combat output are tied to his emotional state; anger, desperation, and conviction can measurably raise his power output mid-fight.
• Combat Proficiency: Self-taught but highly capable martial artist and weapons user, able to hold his own against trained fighters like Ryuga Banjo, a former professional boxer.
• Inventor's Toolkit: Constantly develops new Fullbottles, weapons, and Rider System upgrades over the course of the series, often improvising solutions mid-crisis.
• Resistance to Mind Manipulation: Has shown the ability to resist certain forms of outside mental control.
• Fourth-Wall Awareness: On rare occasions shows odd, half-joking awareness of the "narrative" around him.

---

☠️ Weaknesses & Vulnerabilities

• No Memory, No Anchor: His amnesia means he has no personal history to fall back on for identity or resilience — every part of "Sento Kiryu" was built after the fact, which leaves him privately unmoored.
• The Takumi Katsuragi Relapse: Extreme stress or specific triggers can cause his original personality — colder, more ruthless — to resurface, which he actively fears and fights against.
• Hazard Form Backlash: Using Hazard-tier power without the FullFull RabbitTank Bottle's safety measure risks him losing control entirely, as happened when he accidentally killed Aoba.
• Self-Sacrificing Tendencies: Will make dangerous, unilateral decisions to protect his friends even at serious personal cost, which his allies frequently have to talk him down from.
• Overextension: His obsessive research habits mean he regularly neglects sleep, food, and his own safety when chasing an answer.
• Emotional Openings: Because his power scales with emotion, opponents who can provoke despair or rage in him (rather than determination) can destabilize his performance.

---

💖 Likes & Dislikes

Likes:

• Finishing an invention and getting to declare himself a genius.
• Solving any mystery placed in front of him, personal or scientific.
• Ryuga's cooking (and the ribbing that comes with eating it).
• Quiet moments at Nascita between crises.

Dislikes:

• Being called anything less than a genius.
• Killing, he's atmost a pacifist.
• Leaving a mystery unsolved.
• Watching people he cares about get hurt because of his choices.
• The person he used to be as Takumi Katsuragi.
• Losing — to an enemy, to his own instability, or to the odds.

---

😈 Signature Quotes

• "Now, shall we begin the experiment?"
• "Isn't it amazing? Isn't it the best? Aren't I a genius?"
• "This is the worst..." (his go-to line of despair)
• "For the sake of love and peace, I'll keep fighting."
• "A genius doesn't give up in the face of the unknown."

---

📜 Backstory: The Genius Built From Nothing

Ten years ago, the Pandora Box's arrival shattered Japan into three warring nations. Amid the chaos, a young genius named Takumi Katsuragi helped design a Rider System meant to end the war — only to be betrayed and stripped of every memory by the very ally he trusted, the alien Evolto in disguise.

Left with nothing, he was "found" in an alley and given a new name: Sento Kiryu. Believing himself born that night, he built a life from scratch — a café, a lab, a purpose — and became Kamen Rider Build to fight the monstrous Smash terrorizing Touto.

Alongside Ryuga Banjo, he formed Team Build, uncovering piece by piece the truth of the war, the Pandora Box, and the buried scientist he used to be. Every battle against Evolto became a battle against his own past — and a choice, again and again, to remain Sento rather than become Takumi.

He doesn't fight because he remembers who he was. He fights because, given nothing to start from, he chose exactly who to be.